Heavy-duty carriage assemblies are used in heavy-duty plate fabrication where a tool has to be guided along the edge of a plate for surface preparation, along a portion of the surface of the plate to remove defects, or to support a torch to butt weld plates together as in fabrication of marine vessels and the like. The Arcair Company of Lancaster, Ohio offers such a device for sale under the designation one-half ton machine carriage as illustrated in their brochure entitled "Arcair Travel Systems." The heavy-duty carriage described in the foregoing brochure is a four wheel drive device that requires parallel tracks which support the driven wheels and which guide the carriage along its path. Such a carriage does an excellent job, however, because the rails must be maintained in parallel alignment to the edge of the plate or defect, alignment of such a device before the fabrication operation begins is a problem. Heavy-duty carriages are a complement to the lighter carriages such as described in the foregoing brochure and sold under the trademark CLIMBER.
U.S. Pat. No. Re. 28,121 describes one type of light-duty carriage which features a plurality of swiveled wheels which mount against the edges of a track which is magnetically coupled to the workpiece for guiding the carriage. Motive power is provided by a rack on the track which mates with a gear drive on the carriage. Such carriages are very successful for use in the flame cutting of metallic workpieces.
Three wheeled light-duty carriages wherein the supporting and driven wheels are aligned on parallel tracks are disclosed in U.S. Pat. Nos. 1,320,687 and 1,867,047. These devices rely upon parallel tracks which, in turn, must be aligned parallel to the direction of travel of the metal-working tool (e.g. flame cutting torch) in order to achieve the intended purpose.
U.S. Pat. Nos. 2,283,347 and 2,466,143 disclose light-duty carriages wherein a single rail in the form of an angle iron is utilized as the guide rail for the carriage. In both of these devices, the carriage support mechanism relies upon the wheels riding on the rail to support the carriage and the torch. In both cases a friction drive is used to propel the carriage along the workpiece.